Referring to FIGS. 1 and 2, a conventional switched reluctance motor device includes a reluctance motor 1 and a driving circuit 2. The reluctance motor 1 includes a stator 11 having eight projecting poles (A, A′, B, B′, C, C′, D, D′) , a rotor 12 disposed within the stator 11 and having six salient poles (a, a′, b, b′, c, c′), and four phase windings that are respectively wound around radially opposite pairs of the projecting poles (A-A′, B-B′, C-C′, D-D′) of the stator 11 (hereinafter, phase windings (A″, B″, C″, D″) are used). Each of the phase windings (A″, B″, C″, D″) has a first winding segment (L1) and a second winding segment (L2) respectively wound around the projecting poles of the corresponding radially opposite pair.
The driving circuit 2 is electrically coupled to a direct current (DC) power source (Vdc), and includes four bridge arms 21-24 electrically coupled in parallel with the DC power source (Vdc), and respectively corresponding to the phase windings (A″, B″, C″, D″). Each of the bridge arms 21-24 includes a first switch (Qu) electrically coupled between a positive terminal of the DC power source (Vdc) and a first end of a corresponding phase winding (A″, B″, C″, D″), a second switch (Qn) electrically coupled between a negative terminal of the DC power source (Vdc) and a second end of the corresponding phase winding (A″, B″, C″, D″), a first diode (D1) having an anode that is electrically coupled to the negative terminal of the DC power source (Vdc) and a cathode that is electrically coupled to the first end of corresponding phase winding (A″, B″, C″, D″), and a second diode (D2) having an anode that is electrically coupled to the second end of corresponding phase winding (A″, B″, C″, D″)and a cathode that is electrically coupled to the positive terminal of the DC power source (Vdc).
The driving circuit 2 sequentially switches the phase windings (A″, B″, C″ and D″) to a magnetizing state. Referring to FIGS. 1 to 3, as an example, in a first basic cycle, the first and second switches (Qu,Qn) of the bridge arm 21 that correspond to the phase winding (A″) conduct, such that the first and second winding segments (L1, L2) of the phase winding (A″) are electrically coupled to the DC power source (Vdc), and the corresponding projecting poles (A, A′) generate magnetic attractions that cause movements of the salient poles (a, a′) toward the projecting poles (A, A′). Then, in a second basic cycle, the first and second switches (Qu, Qn) of the bridge arm 21 becomes non-conducting, and the first and second switches (Qu, Qn) of the bridge arm 22 conduct, such that the first and second winding segments (L1, L2) of the phase winding (B″) are electrically coupled to the DC power source (Vdc), and the corresponding projecting poles (B, B′) generate magnetic attractions that cause movements of the salient poles (a, a′) toward the projecting poles (B, B′). Similarly, the phase windings (C″, D″) are subsequently and sequentially switched to the magnetizing state, to thereby drive clockwise rotation of the rotor 12. In contrast, when the phase windings (A″, B″, C″, D″) are switched to the magnetizing state in a sequence of (D″), (C″), (B″), and (A″), the rotation of the rotor 12 may be driven in a counterclockwise direction.
However, referring to FIG. 4, at the end of each basic cycle, e.g., when the first and second switches (Qu, Qn) of the bridge arm 21 are switched to non-conducting, a transient counter-electromotive force (e1, e2) may be generated on each of the first and second winding segments (L1, L2) of the phase winding (A″), resulting in a large current flowing toward the DC power source (Vdc) through the first and second diodes (D1, D2) of the bridge arm 21, and in a high-voltage impact on the DC power source (Vdc), which may cause over-heating of the DC power source (Vdc) due to an excessively large transient current.